A major problem in the treatment of cancer is the development of resistance to chemotherapy and subsequent relapse. Ultimately, patients may fail to respond to any therapy and exhibit clinical resistance to many drugs. Despite the appearance of multiple drug resistance (MDR) in these patients, little is known about its biochemical expressions. Broad cross-resistance to "natural product" anticancer drugs such as Vinca alkaloids and anthracyclines is a well-documented experimental observation. This MDR is often associated with a high molecular weight cell surface glycoprotein (e.g., gp180) and the decreased ability of cells to accumulate and retain drug. However, the relationship and function of these molecular and pharmacologic features to experimental and, especially, clinical MDR is presently unknown. Long-term goals of this work are to learn the functions, if any, of the resistance-associated molecules and to determine if the molecular alterations linked to MDR play a causative role in its development. To accomplish this, a series of human cell lines having different degrees of resistance to different natural product compounds will be selected. Karyotype analysis will be done on these various lines and their revertants. Further, monoclonal antibodies already developed in this laboratory against MDR "marker" proteins (e.g., gp180) will be used to determine the conditions under which such proteins are found to be associated with MDR. The diminished cellular drug accumulation and retention associated with experimental MDR has been attributed either to the workings of an "active efflux pump" of "broad specificity" or to an energy-dependent mechanism of reduced drug-binding. Experiments to determine the mechanism of this altered cellular pharmacology and its relationship to MDR are proposed. Such studies are important to understand the mechanisms of MDR, and also to develop new chemotherapies to overcome it. In this regard, determining the molecular basis by which verapamil and fluphenazine enhance the cytotoxicity of certain anticancer drugs will also provde insights into the mechanisms of MDR. Finally, antibodies directed against resistance-associated proteins may be able to be conjugated to drugs for highly specific targeted therapy, another goal of this application. An important aspect of this work is that by probing molecular mechanisms of MDR, new targets for chemotherapy and new insights into MDR may be obtained.